1. Field of the Invention
The present invention relates to what is called an FIMS (front-opening interface mechanical standard) system that is used in transferring wafers housed in the interior of a transportation container called a pod between semiconductor processing apparatuses in semiconductor manufacturing process or the like. More particularly, the present invention relates to a load port apparatus used in an FIMS system having a door that is adapted to close/open a lid of a sealed container called an FOUP (front-opening unified pod) or pod in which wafers are housed and a small clean space (or mini-environment) in which a robot arm that transfers wafers into/from the pod is provided. The load port apparatus to which the present invention relates is adapted to prevent dust from entering the interior of the small clean space. The present invention also relates to a mini-environment system including such a load port apparatus and a semiconductor processing apparatus.
2. Related Background Art
In the past, the semiconductor manufacturing process had been performed in what is called a clean room constructed by establishing a high degree of cleanness in the room in which semiconductor wafers are handled. In recent years, however, in view of an increase in the wafer size and with a view to reduce cost incurred in maintenance of the clean room, a method of keeping clean only the interior of a processing apparatus, a pod (or wafer container) and a small space through which substrates or wafers are transferred between the pod and the processing apparatus has been used.
The pod is composed of a body portion of a substantially cubical shape having shelves provided therein that can hold a plurality of wafers in a parallel and separated state and an opening provided on one side thereof through which wafers can be brought into/out of it, and a lid for closing the opening. Those pods that have an opening portion provided not on the bottom but on one lateral side thereof (i.e. the front side to be opposed to the small space) are collectively called FOUP (front-opening unified pod). The present invention is mainly directed to technologies in which the FOUP is used.
A system provided with the above mentioned small space (mini environment) has a first opening opposed to the opening of the pod, a door for closing the first opening, a second opening provided on a semiconductor processing apparatus, and a transferring robot that is adapted to reach into the interior of the pod through the first opening to pick up a wafer and transfer it into the processing apparatus through the second opening. The system provided with the small space also has a support table that supports the pod in such a way that the pod opening is placed just in front of the door.
On the top face of the support table are positioning pins to be fitted into positioning holes provided on the bottom surface of the pod and a cramping unit adapted to engage with a portion to be cramped provided on the bottom surface of the pod to fix the pod to the support table. Typically, the support table is adapted to be movable toward and away from the door over a predetermined distance. When the wafers in a pod are to be transferred into the semiconductor processing apparatus, the support table on which the pod is placed moves toward the door until the lid of the pod comes into abutment with the door, and then after abutment, the lid is held and removed by the door, whereby the opening of the pod is opened. By this process, the interior of the pod and the interior of the processing apparatus are bought into communication with each other through the small space to allow wafer transferring operations that will be performed repeatedly. All of the support table, the door, the first opening, a mechanism for opening/closing the door and walls partly defining the small space and having the first opening are included in what is referred to as an FIMS system (front-opening interface system) or a load port apparatus. What is collectively referred to as a mini-environment system includes a load port apparatus, a pod and a semiconductor processing apparatus to which the load port apparatus is attached.
In such systems, generally, the pressure in the interior of the small space is designed to be higher than the pressure of the ambient space (which will be hereinafter referred to as the exterior space) to prevent dust or particles present in the exterior space from entering the interior of the small space. In other words, when the aforementioned first opening is open, a flow of air from the interior of the small space to the exterior space is generated so that dust or the like is always blown to the exterior space by the air flow. When the door is opened or closed, turbulence of air flow may occur near the first opening. Such turbulence of air flow may lead to entry of dust into the interior of the small space. To prevent such turbulence of air flow from occurring, in a load port apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-373927 or Japanese Patent Publication No. 3581310, clearance is left around the door when the door is at the position for closing the first opening so that the interior of the small space and the exterior space are in communication with each other through the clearance.
The pressure in the interior of the small space is increased generally by introducing air from the exterior space into the interior of the small space using a fan provided in the upper portion of the small space. If the pressure difference between the interior of the small space and the exterior space becomes excessively large, there is a risk that entry of air into the pod or undesired turbulence of air flow may occur. In view of this, it is preferred that the pressure difference be kept small. Furthermore, it is preferred to keep the outflow of air from the small space constant while keeping the aforementioned small pressure difference. In the semiconductor manufacturing industry, the size of the wafers has been increased in recent years, and wafers having a diameter of 300 mm are to be processed. Accordingly, the volume of the small space has also been increased. Accordingly, in the case of the apparatus that uses a fan, it may become difficult to keep the aforementioned small pressure difference both in the relatively upstream position and relatively downstream position in the air flow and to keep the air flow rate constant. When the pressure difference is controlled to be small, the air flow condition in the clearance at the upper portion of the door in the upstream and that in the clearance at the lower portion of the door in the downstream may probably differ from each other, as discussed in Japanese Patent Application Laid-open No. 2002-373927.